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The Lambda ratio (λ) has been widely used as an indicator of the lubricant regime in an operating contact within either bearings or gear sets. λ is determined when the lubricant film thickness (h) within the contact is divided by the composite roughness (σ) of the two surfaces forming the contact. Recommendations of an appropriate film thickness equation and surface roughness values are provided to calculate modified lambda ratio (λm) that better represents the lubricant regime within bearings or gears. Bearing performance, especially as related to fatigue life, has increased significantly in recent years. This is primarily due to cleaner steels but includes the influence of better surface finishes and bearing internal geometries. With λm, and an understanding of how contact fatigue damage mode relates to a wide range of λm values, it may be possible to transfer the advances in bearing performance to other system components such as gears.

In an earlier paper the primary factors that relate debris to bearing fatigue performance were discussed. It was recognized that it is the largest debris particles in a lubricant system that can influence fatigue life by the denting they produce. Some recent tests are described that provide an approximate relationship of particle size to dent size. An additional analysis of dent shape (primarily slope of the side wall) indicates that the severity of slope is a measure of the dent as a surface stress riser and thus its influence on bearing fatigue life. Comments concerning debris accessibility to a contact and a method to evaluate material differences in tolerating debris are also included.